KR20030088599A - Optical fiber for optical amplifier and production method of the same - Google Patents

Abstract

PURPOSE: An optical fiber for an optical amplifier and a manufacturing method thereof are provided to reduce the manufacturing cost by doping a core layer with a mixed solution of rare earth and metal ions using a solution doping method. CONSTITUTION: In order to manufacture an optical fiber using MCVD(Modified Chemical Vapor Deposition), a clad layer and a second core layer are formed in a silica substrate tube(S10). A first core layer is formed on an inner surface of the second core layer(S20). The first core layer forms a partially-sintered layer that provides a host with respect to a Tm¬3+ ion and a metal ion. A mixed solution of the Tm¬3+ and metal ions is uniformly doped on the first core layer(S30). After completing the doping of the mixed solution, an optical fiber is manufactured by wire-drawing a glass rod containing the Tm¬3+ and metal ions(S40).

Description

Optical fiber for optical amplifier and manufacturing method {OPTICAL FIBER FOR OPTICAL AMPLIFIER AND PRODUCTION METHOD OF THE SAME}

The present invention relates to an optical fiber for an optical amplifier and a manufacturing method for applying the optical transmission system in the S band region (1430nm ~ 1530nm), unlike the conventional optical fiber of the optical amplifier of the S band, the preform component of the optical fiber silica-based glass The optical fiber is capable of optical amplification in the S-band region by depositing rare earth and metal ions on the first core layer formed on the inner surface of the core layer by the MCVD (Modified Chemical Vapor Deposition) method and the solution doping method, which are commercial internal vapor deposition methods. To manufacture.

In general, optical communication is divided into a transmitter part for converting an electrical signal into an optical signal and a receiver part for converting an optical signal into an optical signal and an optical signal for transmitting the optical signal.

The optical fiber, a passive device that transmits optical signals, absorbs optical signals due to electron transition by cations of glass in the case of short wavelengths, and absorbs optical signals due to molecular vibration in the case of long wavelengths. Only wavelengths can be used for optical communication.

However, this area is also affected by impurities such as OH ^- groups and transition metals contained in the preform glass, so that only the band around 1300 nm wavelength and 1550 nm wavelength are used for optical communication.

Meanwhile, the 1550 nm band is mainly used for long-distance transmission where the loss of silica glass optical fiber is the smallest, and transmission loss is important. The 1300 nm band is mainly used for short-range optical transmission as the zero dispersion wavelength of silica glass optical fiber. (John B. MacChensey , David J. DiGiovanni, J. Am. Ceram.Soc., 73 [12], 1990)

However, the silica glass optical fiber transmits light but also absorbs light. The loss due to the absorption is accumulated, and the intensity of the signal light decreases exponentially as the transmission distance becomes longer.

To amplify this reduced signal, an amplifier that amplifies the intensity of the signal light should be installed every several decades of the optical fiber network. The amplifier first converts the optical signal into an electrical signal and amplifies it, and then transmits it back to the optical signal. However, due to the effects of error in the amplification process and the delay time for amplifying the optical signal, it is not effective and it has not been put to practical use.

Thus, instead of the amplification method of converting and amplifying an optical signal into an electrical signal and then transmitting the optical signal, an optical fiber amplifier that amplifies an optical signal without converting the optical signal has been actively studied.

The first fiber amplifiers were based on barium crown glass, and optical amplifiers with neodymium were studied (CJ Koester and E. Snitzer, Appl. Opt., Vol. 3, pp 1182-1186. , 1964)

Later, fiber amplifiers had high gains and low losses in the late 1980s, and Erbium doped fiber amplifiers (EDFA) were developed in which the lowest loss region of silica fibers amplified the 1550 nm band wavelength. (WJ Miniscalco, J. Lightwave Technol., Vol. 9, pp234-250, 1991).

However, the recent explosive increase in the amount of information transfer has caused a need for a fiber amplifier that can be used in a new wavelength band because the available wavelength band is saturated with the conventional wavelength division multiplexing (WDM) technology.

First, the available wavelength band was extended to 1600nm, which is longer than the 1550nm wavelength band by using the Gain-Shifted EDFA. However, this also saturates the need for an optical fiber amplifier that can be used in other wavelength bands.

On the other hand, the 1480nm band adjacent to the 1550nm band is easily accessible, the optical fiber amplifier that can be used in the S-band (1430nm to 1530nm) is currently being researched and developed optical fiber for optical amplifiers containing Tm ³⁺ ions.

Fluorescence generated during the transition from the ³ H ₄ level of Tm ³⁺ to the ³ F ₄ level has a central wavelength of 1480 nm, enabling optical amplification in S-band.

However, the transition of the Tm ³⁺ is ³ H _4, since the distance between the lower levels of ³ H ₅ level in less to about 4200cm ^-1, having a lattice vibration energy of about 1100cm ^-1 silica glass in the ^three levels in H ₄ the transition to the ³ F ₄ levels, it is difficult to obtain fluorescence of 1480nm generated.

That is, a transition does not occur from the ³ H ₄ level to the ³ F ₄ level, but a thermal transition occurs directly to the lower level ³ H ₅ level and is absorbed by the lattice vibration in the glass base material.

Thus it is trying to fluorescence of 1480nm by the transition of the current research and development direction of the lattice vibration energy in the small fluoride-based glass and the sulfide glass as a ³ F ₄ level in the ³ H ₄ level of the Tm ^3+.

Recent research results from T. Kasamatsu's paper (Laser-Diode-Pumped Highly Efficient Gain-Shifted Thulium-Doped Fiber Amplifier Operating in the 1480-1510nm Band, IEEE Photonics Technology Letters, vol. 13, No. 5, 433-435 , (Fluorescence) of 1480 nm was obtained using fluoride-based glass as a known material.

And YB Shin's paper (Multiphonon and cross relaxation phenomena in Ge-As (or Ga) -S glasses doped with Tm ³⁺ , Journal of Non-Crystalline Solids, 208, pp 29-35, 1996) The fluorescence expression of and its mechanism was described.

In another study, U. S. Patent No. 6266181 proposed an optical fiber amplifier using tellurite-based glass as a known material. According to Choi's paper (Influence of 4f absorption transitions of Dy3 + on the emission spectra of Tm3 + -doped tellurite glasses, Journal of Non-Crystalline Solids, 276, pp 1-7, 2000), fluorescence of 1480 nm was obtained.

However, such fluoride-based glass, sulfide-based glass, and tellurite glass have many difficulties in connection with existing silica fibers.

That is, if the refractive index is high, when connected with the existing silica optical fiber, the signal light may not be transmitted and may be lost due to scattering. The melting point of the fluoride glass and the sulfide glass and the melting point of the silica optical fiber are large so that melting may be performed. Connection is difficult.

In addition, since the raw materials are melted in a crucible during the manufacture of the optical fiber and manufactured by melting the optical fiber, the possibility of contamination by impurities such as OH ^- groups and transition metals is high, and the possibility of optical fiber defects is also very high.

For this reason, the light loss reaches about 200 dB / m, and chemical durability such as penetration of OH ^- groups of the manufactured optical fiber is also poor, which makes it difficult to be practical.

Therefore, the present invention was created to solve the above problems, and an object of the present invention is to dope the core layer with a mixed solution of rare earth and metal ions using a solution doping method, which is generally used, and thus, S-band. (1430nm to 1530nm) to provide a low-cost manufacturing optical fiber that provides a stable optical characteristics and convenience.

One of the other objectives of the present invention is to provide an optical amplifier optical fiber which can obtain a high and stable doping concentration and obtain appropriate optical amplification characteristics by adjusting the concentration of doping ions and by adjusting the refractive index profile. In providing.

In addition, the present invention solves the problem that Tm ³⁺ ions fluoresce in the 1480 nm band only in the fluoride-based glass and sulfide-based glass having the above-described low lattice vibration energy, thus enabling optical amplification in the 1480 nm band. It is to provide an optical fiber.

1 is a view showing a schematic configuration of an optical fiber for an optical amplifier according to the present invention.

Figure 2 is a flow chart showing a schematic method of manufacturing an optical fiber for an optical amplifier according to the present invention.

3 shows the energy level of Tm ³⁺ ions.

Figure 4 is a view showing a fluorescence measuring device of the preform for the optical amplifier prepared according to Example 1 of the present invention.

FIG. 5 is a diagram showing 1480 nm fluorescence of a Tm ³⁺ ion and a fluorescence emission spectrum of 1800 nm by irradiating a laser having a wavelength of 800 nm to a preamplifier for an optical amplifier prepared according to Example 1 of the present invention.

6 is a view showing an absorption spectrum in the wavelength range of 600 nm to 850 nm of Tm ³⁺ in the optical amplifier preform manufactured according to Example 1 of the present invention.

7 is a view showing absorption spectra in a wavelength range of 1150 nm to 1250 nm of Tm ³⁺ in the optical amplifier preform manufactured according to Example 1 of the present invention.

* Description of the symbols for the main parts of the drawings *

1: substrate tube 2: cladding layer

3: second core layer 4: first core layer

11: Ar laser 12: Ti-Sapphire laser

13: chopper 14: optical fiber preform

15: monochromator 16: monochromator controller

17: InSb detector 18: preamplifier

19: Lock-in amplifier 20: Computer

The present invention for achieving the above object includes a silica, germanium, fluorine as a base material in the optical fiber comprising a substrate tube, a cladding layer and a core layer so that the optical fiber is used as an optical amplifier in the region of 1430nm to 1530nm And a first core layer doped with impurities including Tm ³⁺ ions and metal ions at a central portion of the core layer; and a second core layer formed on an outer circumferential surface of the first core layer and not doped with impurities. It provides an optical fiber for an optical amplifier, characterized in that.

In the present invention, the optical fiber is a step of forming a clad layer and a second core layer inside the silica substrate tube using the MCVD method; Forming a first core layer on the inner surface of the second core layer, the first core layer forming a partially sintered layer providing a host to Tm ³⁺ ions and metal ions; Uniformly doping a solution in which a Tm ³⁺ ion and a metal ion are mixed in the first core layer on which the partially sintered layer is formed; After the solution doping is completed, it is preferable to prepare a glass rod containing Tm ³⁺ ions and metal ions by disintegrating the base material at a high temperature, and then preparing the glass rod with a constant diameter optical fiber.

In addition, the present invention provides an optical amplifier using the optical fiber described above.

Hereinafter, the configuration of the present invention will be described in detail based on the accompanying drawings.

In addition, this embodiment is not intended to limit the scope of the present invention, but is presented by way of example only.

1 is a view showing a schematic configuration of an optical amplifier optical fiber according to the present invention, Figure 2 is a flow chart showing a schematic manufacturing method of the optical amplifier optical fiber according to the present invention.

As shown, the optical amplifier optical fiber according to the present invention includes a first core layer 4 formed at the center of the base material, a second core layer 3 formed on the outer circumferential surface of the first core layer 4, and And a cladding layer 2 formed on the outer circumferential surface of the second core layer 3 and a substrate tube 1 formed on the outer circumferential surface of the cladding layer 2.

That is, in the present invention, silica, germanium, and fluorine are used as base materials so that the optical fiber is used as an optical amplifier in the region of 1430 nm to 1530 nm, and Tm is formed in the center of the core layer.³⁺ion And a first core layer 4 doped with an impurity including metal ions, and a second core layer not doped with impurities is formed on an outer circumferential surface of the first core layer 4.

In this case, it is preferable to additionally include one or two or more rare earth ions selected from the group consisting of Ho, Tb, Eu, Dy, Yb, Er, and Pr as the doped impurities.

In addition, any one or two or more of the group consisting of Al, La, and Te may be selected and used as the metal ions. Preferably, the ion of Te is used as the metal ion.

Meanwhile, the core layer of the present invention is divided into a first core layer 4 doped with impurities and a second core layer 3 not doped with impurities, but only one single layer doped with impurities is formed. It is also possible.

In addition, it is preferable to use a laser and a laser diode of a wavelength at which absorption of Tm ³⁺ ions occurs as an excitation light source of the optical amplifier optical fiber.

The manufacturing method of the optical fiber according to the present invention described above is as follows.

First, silicon tetrachloride, germanium tetrachloride, and fluorine are supplied to the silica substrate tube 1 in a gaseous state, and the substrate tube 1 is rotated and heated while moving an external heating source to the left and right directions, thereby heating the substrate. By sintering transparent to the inner wall of the tube 1 to cause the deposition of fine particles, the clad layer 2 is formed such that the refractive index is equal to the cladding layer 2 or the substrate tube 1 which is about 0.2% smaller than the substrate tube 1. Let's do it.

The second core layer 3 supplies silicon tetrachloride and germanium tetrachloride in a gaseous state, rotates the substrate tube 1 as described above, and heats the external heating source while moving in the left and right directions. By sintering the inner wall of the cladding layer 2 to cause fine particles to be deposited, the second core layer 3 having a refractive index of about 0.2% to 1.2% higher than that of the substrate tube 1 is deposited.

As described above, when the preparation step (S10) of forming the cladding layer 2 and the second core layer 3 inside the silica substrate tube 1 to manufacture the base material of the optical fiber by the MCVD method, the second, The first core layer 4 is deposited in the same way as the core layer 3 is deposited. The difference between the second core layer 3 and the deposition method is that the external heating is performed at a high temperature to achieve complete sintering. Instead, by lowering the temperature, partial sintering is performed to provide a host for impurities (S20).

Such hosts must be optimized so that the chemicals deposited are porous without impurities and create bubbles.

The reason for the partial sintering as described above is that when sintering completely without partial sintering, it is difficult to form a space in the first core layer 4 and doping is not actively performed.

After the step (S20) of forming a partial sintered layer to provide a host for the Tm ³⁺ ions and metal ions on the inner surface of the core layer, that is, the first core layer (4), Tm on the base material on which the partial sintered layer is formed The solution mixed with ³⁺ ions and metal ions is maintained for about 1 hour so that the solution is uniformly doped in the partially sintered layer (S30).

In this case, the solution doped in the first core layer 4 may include rare earth metal ions selected from the group consisting of Pr, Er, Nd, Eu, Tb, Dy, Ho, Yb in addition to Tm, wherein the metal ion Any one or two or more selected from the group consisting of Al, Te, and La are made by mixing metal ions.

The Tm ³⁺ ions, rare earth metal ions and metal ions are prepared by adding a rare earth metal ion and a metal ion such as water, acetone or alcohol in a solvent capable of dissolving.

After the solution doping step (S30), the doping solution is dried and the partially sintered layer provided as a host is completely sintered, and then the base material is collapsed at a high temperature to obtain the glass rod containing the Tm ³⁺ ions and metal ions. By manufacturing and cutting the fiber with a constant diameter of the optical amplifier to produce an optical fiber (S40).

The optical fiber manufactured in this way has a diameter of the core layer of about 1 to 6㎛, the diameter of the optical fiber is 125㎛, by controlling the diameter and refractive index of the core layer, having a cutoff wavelength of less than 1250nm. To do that.

That is, as a known technique Is the same as

Where a is the radius of the core, n ₁ is the refractive index of the core, n ₂ is the refractive index of the clad, Represents the wavelength of light, to be.

Where V is less than 2.405 The value is the blocking wavelength.

therefore, By controlling the size and refractive index of the core through the equation to control the desired blocking wavelength.

Meanwhile, as rare earth ions doped in the first core layer 4 of the optical fiber, Tm ³⁺ ions which emit 1480 nm of fluorescence with a transition from ³ H ₄ levels to ³ F ₄ levels, which are lower levels, are added and are optically amplified. It is desirable to add Al, Te, La and metal ions that widen the band and reduce the lattice vibration energy of the base metal.

In this case, the content of the Tm ³⁺ ions is preferably 100 ~ 20,000 ppm, the content of the metal ions is preferably 0.01 ~ 10mol%.

That is, the first core layer 4 in the wavelength band of 1430nm ~ 1530nm in order to prevent the energy absorbed by the transition from the ³ H ₄ level of Tm ^{3 +} to ³ H ₅ level by the lattice vibration to the base material It is preferable to be doped with ions, and the first core layer 4 is doped with metal ions Al or La to increase the solubility of the rare earth ions doped in the wavelength range of 1430 nm to 1530 nm and to increase the optical amplification range. desirable.

In addition, since the fluorescence lifetime of the ³ F ₄ level, which is a lower level of Tm ³⁺ , is longer than the fluorescence lifetime of the ³ H ₄ level which expresses 1480 nm fluorescence, spontaneous fluorescence expression is difficult, and thus, the first core layer 4 is doped. solution has a Tm ³⁺ in the ³ F ₄ level of the lower energy level of the ions is transferred to the other rare earth metal ion, which serves to reduce the fluorescent lifetime of the ³ F ₄ level Ho, Dy, Eu, Tb ions by energy transfer is added to .

At this time, the content of the rare earth ions added is preferably 0.01 ~ 5 mol%.

That is, as mentioned in the prior art, the distance between the ³ H ₄ level and the ³ H ₅ level of the Tm ³⁺ ion is about 4200 cm ⁻¹ (John B. MacChensey, David J. DiGiovanni, J. Am. Ceram. Soc , 73 [12], 1990) When fluorescence emission is induced by using silica glass having a lattice vibration energy of about 1100 cm ⁻¹ , transition from the desired ³ H ₄ level to ³ F ₄ level does not emit fluorescence, Heat is absorbed into the matrix material by the lattice vibration.

In order to solve this problem, fluoride glass and sulfide glass have been studied. US Pat. No. 6266181 proposes a fiber amplifier using tellurite glass as a known material, and YG Choi's paper (Influence) of 4fabsorption transitions of Dy3 + on the emission spectra of Tm ³⁺ -doped tellurite glasses, Journal of Non-Crystalline Solids, 276, pp 1-7, 2000).

However, if the refractive index of the known material is high, when connected with the existing silica optical fiber, the signal light may not be transmitted and may be lost due to scattering, and the melting point of the fluoride glass, the sulfide glass, the tellurium glass, and the silica optical fiber may be lost. Since melting point difference is about 500 degreeC or more, connection through melting is difficult.

In addition, since the optical fiber is manufactured by melting a raw material into a crucible and then cutting the optical fiber, there is a high possibility of contamination by impurities such as OH ^- and a transition metal, and an optical fiber defect is also very likely.

Therefore, in order to fabricate a silica glass optical fiber having a low lattice vibration energy, the present invention dopes Te, Al, and La together to make the local environment around the rare earth into a glass environment other than silica glass, thereby making the 1480 nm band in the silica optical fiber. Fluorescence was obtained.

Inde Figure 3 shows an energy level diagram of the Tm ³⁺ ions, the excitation light of 800nm Tm ³⁺ ions are excited to ³ H ₄ level in the ground state, the transition consists of a ³ F ₄ level to me fluorescence of 1480nm do. In addition, the transition from the ³ F ₄ level to the ground state of the ³ H ₆ level gives a fluorescence of 1800nm.

Then, the excitation light of the 1064nm Tm ³⁺ ions is excited by ³ H ₅ level, and transition back by the lattice vibration in spontaneously ³ H ₄ level then this is made a transition to the ³ F ₂ level ³ F ₄ level Fluorescence of 1480 nm occurs.

As described above, the present invention provides an optical amplifier optical fiber in which a rare earth ion is doped in the first core layer 4 of silica glass and another metal ion is doped, and the optical fiber is a modified chemical vapor deposition (MCVD). Tm ³⁺ ions and other metal ions are doped into the first core layer 4 by a conventional solution doping method.

On the other hand, it is possible to produce an optical amplifier having a well-known configuration using the above-described optical fiber, the excitation light source used as the optical amplifier is to use a laser and a laser diode of the wavelength at which the absorption of Tm ^{3 +} ions occurs. desirable.

Example 1

4 is a view showing a fluorescence measuring device of the optical amplifier preform prepared according to Example 1 of the present invention, the optical fiber preform 14 to which Tm, Tb, Al, Te ions are added to the core, Fit specimens were prepared to measure fluorescence spectra and absorption spectra.

At this time, the size of the specimen is 15mm in diameter, 20mm in height, the size of the core is 1.13mm, the concentration of Tm ³⁺ ions is 0.16wt% as measured using Electron Probe Micro Analysis (EPMA). And, the cross section was optically polished to less than 1㎛, the experiment was conducted at room temperature.

Looking specifically at the experimental apparatus of Example 1, the Tm ^{3 +} ions are excited with an 800 nm wavelength Ti-Sapphire laser 12 driven by an Ar laser 11 having a 488 nm wavelength to excite light with a monochromator 15. Was separated, and the signal light was measured with an InSb detector 17, and a fluorescence spectrum was obtained using a computer 20.

That is, the fluorescence which spontaneously expresses by injecting the Ti-Sapphire laser 12 light source having a wavelength of 800 nm and the incident light intensity of 1.3 W into the core portion of the manufactured preform 14 from 550 nm to 2800 nm placed vertically from the incident light. Fluorescence spectra were obtained using an InSb detector (EG & G, 11) capable of detecting light.

In addition, the monochromator 9 is a 1/4 m, and the chopper 7 and the lock-in-amplifier 13 rotated at 100 times / second to amplify the signal from the detector 17. It was.

In addition, the absorption spectrum was measured by using a Lambda 900 UV / VIS / NIR spectrometer of PerkinElmer by processing the base material in the shape of a disk.

In this case, reference numeral 16 is a monochromator controller, and reference numeral 18 is a preamplifier.

FIG. 5 is a diagram showing a 1480 nm fluorescence of a Tm ³⁺ ion and a fluorescence emission spectrum of 1800 nm by irradiating a laser having a wavelength of 800 nm to a preamplifier for an optical amplifier prepared according to Example 1 of the present invention.

And, Figure 6 is a view showing the absorption spectrum in the 600nm to 850nm wavelength band of Tm ³⁺ in the optical amplifier preform manufactured according to Example 1 of the present invention, ³ H ₄ level of Tm ^{3 +} ion in the 800nm wavelength band You can see thermally connected ³ F ₃ and ³ F ₂ levels from 650 nm to 700 nm.

In addition, Figure 7 is a view showing the absorption spectrum in the wavelength range of 1150nm to 1250nm of Tm ³⁺ in the optical amplifier preform manufactured according to Example 1 of the present invention, ³ H ₅ level of Tm ^{3 +} ion in the band 1210nm Can be seen.

On the other hand, additional advantages and modifications of the present invention will be readily apparent to those skilled in the art.

Therefore, various modifications and variations are possible to those skilled in the art within the equivalent scope of the technical concept of the present invention and the claims to be described below.

As described above, the optical fiber for an optical amplifier according to the present invention can be used in the band from 1430 nm to 1530 nm, is inexpensive for manufacturing, and has an effect of presenting stable optical characteristics and convenience.

In addition, a high and stable doping concentration can be obtained, and an appropriate optical amplification characteristic can be obtained by adjusting the concentration of the doping ions and the refractive index profile.

In addition, the present invention solves the problem that Tm ³⁺ ions fluoresce in the 1480 nm band only in the fluoride-based glass and sulfide-based glass having low lattice vibration energy, thereby providing an optical amplifier silica optical fiber capable of optical amplification in the 1480 nm band. It is effective.

Claims (10)

In an optical fiber comprising a substrate tube, a cladding layer and a core layer, It includes silica, germanium, fluorine as a base material so that the optical fiber is used as an optical amplifier in the region of 1430nm to 1530nm, A first core layer doped with an impurity including Tm ³⁺ ions and a metal ion in a central portion of the core layer; The optical amplifier optical fiber, characterized in that formed on the outer circumferential surface of the first core layer and composed of a second core layer which is not doped with impurities. The method of claim 1, Optical fiber for an optical amplifier, characterized in that the doped impurities additionally include any one or two or more rare earth ions selected from the group consisting of Ho, Tb, Eu, Dy, Yb, Er, Pr. The method of claim 1, The optical fiber for an optical amplifier, characterized in that to use any one or two or more selected from the group consisting of Al, La, Te as the metal ion. The method of claim 1, Optical fiber for an optical amplifier, characterized in that to maintain a cutoff wavelength of 1250nm or less by controlling the diameter and the refractive index of the core layer. The method of claim 1, And the first core layer and the second core layer are formed of a single layer doped with impurities. The method according to any one of claims 1 to 5, An optical amplifier optical fiber, characterized in that for the excitation light source of the optical amplifier optical fiber using a laser and a laser diode of a wavelength at which the absorption of Tm ^{3 +} ions occurs. The optical amplifier using the optical fiber of any one of Claims 1-5. Forming a cladding layer and a second core layer in the silica substrate tube in order to manufacture the base material of the optical fiber by using the MCVD method (S10); Forming a first core layer on the inner surface of the second core layer, the first core layer forming a partially sintered layer providing a host to Tm ³⁺ ions and metal ions; Uniformly doping the solution of a mixture of Tm ³⁺ ions and metal ions in the first core layer (4) having the partial sintered layer (S30); After the solution doping is completed, the substrate is collapsed at a high temperature to produce a glass rod containing the Tm ³⁺ ions and metal ions, and the optical amplifier is characterized in that the optical fiber is produced through the step (S40) of cutting a constant diameter optical fiber Method for manufacturing optical fiber for 9. The optical amplifier of claim 8, wherein any one or two or more rare earth ions selected from the group consisting of Ho, Tb, Eu, Dy, Yb, Er, and Pr are additionally included in the doped impurities. Optical fiber manufacturing method. The method of claim 8, wherein the metal ion is selected from any one or two or more selected from the group consisting of Al, La, Te is used in the optical amplifier optical fiber manufacturing method.